268 IS SILICA A CONSTITUENT OF PLANT FOOD? 



How different the demands for silica are in other crops may 

 be shown by these figures : 



Buckwheat 5.5% Silica. 



Peas 6.8% „ 



Beans . . . 7.3% „ 



Some of the seeds of these water cultures were put in a 

 germinating dish, and after a few days were observed to 

 germinate. 



We have now completed the life cycle of one of these wheat 

 plants, and have shown the non-essential part silica plays as a 

 nutritive. 



The silica is deposited in the cell membrane and being in the 

 epidermis of the plant, supplies a certain protection from fungi 

 ( rust ) sending its mycelium roots into the leaf. 



I have it on Dr. Hahn's authority that a number of years 

 ago a series of water culture experiments were being carried out 

 at the South African College Chemical Laboratory, when they 

 became attacked by rust, and in two days every plant was over- 

 run with the fungus. This clearly shows that when the plant is 

 deprived of its silica it can offer no resistance to the ravages of 

 such pests as rust. 



Here in South Africa we have a fine sunny climate where 

 everything thrives well, including the pests. 



As to how and to what extent silica in a plant repels the 

 attacks of fungoid growth is indeed a subject offering a wide 

 field for research, and being of such great importance to us' 

 South Africans, surely this matter should be taken up and 

 thoroughly investigated by our biologists. 



It is well known that the silica in soils derived from granitic 

 rocks is less soluble than the silica which is derived from doleritic 

 and basaltic rocks. In the granitic rocks the silica exists as pure 

 quartz, and as trisilicate in felspar and mica, whereas dolerite 

 and basalt do not contain free quartz, and their constituent 

 silicates like hornblende, augite, anorthite, are disilicates and 

 monosilicates. 



Since the silica in the granitic soils is less soluble than silica 

 in the dolerite and basaltic soils, one cannot help thinking that 

 the cereals which are such great silica eaters will take advantage 

 of this when grown on doleritic or basaltic soils, and will contain 

 more silica in the ashes than the cereals grown on granitic soils. 

 If the theory is correct that the presence of silica in the cereals 

 renders the plants more resisting to the attacks of fungoid 

 growth, the cereals grown on dolerite and basaltic soils should 

 suffer less than the cereals grown on granitic soils, provided that 

 climatic and weather conditions are the same. 



These are questions of such economic importance to South 

 Africa that they should receive full attention at the hands of 

 those who are carrying on research in connection with the 

 production of cereals in our country. 



